Immortal time bias
Shengping Yang, Gilbert G. Berdine · The Southwest Respiratory and Critical Care Chronicles · 2022
I am planning a study to evaluate the relationship between infection and mechanical ventilation.Because we are interested in a time-to-event outcome, I am wondering whether there is a potential risk of introducing immortal time bias and how to avoid it.In studies with a time-to-event (survival) outcome, immortal time refers to a period of follow-up during which, by design, death or the event of interest cannot occur.1,2 In general, immortal time could happen in an exposure/treatment group if the subjects need to be followed long enough to experience an exposure or receive a treatment and be event-free prior to the exposure/treatment.